Micromechanical sensors such as rotational rate sensors have been known for a long time. They have one or more micromechanically structured, seismic oscillating masses which are subjected to a controlled periodic movement (excitation movements) in a plane (excitation vibrational plane). These seismic oscillating masses are structured and mounted in such a way that they or parts thereof are also movably suspended in a plane perpendicular to the excitation vibrational plane. This plane is referred to as the detection plane. They also include a detection unit which picks up the displacement of the vibrating mass or masses or parts thereof in the detection plane. Displacement in the detection plane occurs either due to the Coriolis force acting on the moving vibrating masses in the case of linear oscillators, or due to angular momentum conservation in the case of rotational oscillators.
It is also known in the art that a cover section or a cap section may be applied to the corresponding sensor section to create a hermetically sealed sensor interior between the cover section and the sensor section. Such micromechanical sensors require the lowest possible gas pressure in the hermetically sealed sensor interior to achieve a high quality, i.e., low attenuation of the mechanical vibrational structure due to an ambient medium. Such sensors are therefore generally encapsulated in vacuo.
Various approaches are known for connecting sensors and electronic analyzers. In addition to connecting the sensor section and the electronic analyzer via bond wires, integrated embodiments in which the electronics and sensors are manufactured in one manufacturing operation are also known.
Additive integration has also been known for some time. In this method, a sensor structure is applied to a finished electronic chip in a low-temperature process. For example, metals are applied by a galvanic process, or silicon-germanium is applied by a low-pressure deposition process.
Increasing demands on the resolution capability of sensors, and thus on the signal-to-noise ratio of the overall system of sensor section/electronic analyzer, require a reduction in parasitic elements which are caused to a great extent by the feeder lines and bond sites.
One approach to solving this problem involves a monolithic integration of sensor section and electronic analyzer. One disadvantage of this approach is the fact that the sensor process requires a much smaller mask level than does a complex electronic process. Thus, a portion of the chip surface is lost for the electronic function, which is a disadvantage for reasons of cost and space. Furthermore, there is the disadvantage that it is not possible to test the sensor section and electronic analyzer separately, and therefore total yield may be tested only at a relatively high value creation level.
An alternative approach involves additive integration of the sensor section and electronic analyzer. In this case, the sensor section is applied subsequently to a finished analyzer circuit. Parasitic elements may also be reduced significantly by this approach, but only low-temperature processes may be used to manufacture the sensor so as not to damage the electronics. Furthermore, one disadvantage of this approach is that the process window is extremely small, and so far it has not been possible to produce larger components, e.g., rotational rate sensors, because of intrinsic attenuation or voltage gradients.
Furthermore, all approaches mentioned above have the disadvantage that manufacture of the cover or cap section is highly complex, and therefore carries high manufacturing costs.